<Button>:  #parent type, apply to all the buttons
    font_size: 30
    color: 0.3,0.6,0.7,1   #rgb:[-1,1], alpha value = 1: show up
    size_hint: 0.3, 0.5  #width, height: percent

<FloatLayout>:   #apply to any floatlayout
    Button:
        pos_hint: {"x":0.5, "top":1} #{"x", "y", "top", "bottom", "left", "right"}  # 6 keys in a dictionary, with the number between 0,1, showing the percent
        text: "Hello"

    Button:
        id: btn
        pos_hint: {"y":0.3}  #move up from the bottom 30%
        text: "World" if btn.state == "normal" else "Down"
        background_color: [0.3, 0.4, 0.5, 1] if btn.state == "normal" else [0.5, 0, 0, 1]

<Touch>:
    btn: btn  #change the opacity

    Button:
        id: btn  #change the opacity
        text: "My Btn"